1. Field of the Invention
The present invention relates to a secondary battery. More specifically, the present invention relates to a secondary battery having an upper case formed of a metal.
2. Description of the Related Art
With the rapid advance and development in recent years of electronic, information communication and computer industry fields, there is a gradual increase in the use of portable electronic devices. Rechargeable secondary batteries are largely used as a power source for portable electronic devices.
At present, a pack-type battery is widely used as a secondary battery. The pack-type battery is a form of the battery with integration of a bare cell and a protection circuit module (PCM) into one unit. The pack-type secondary battery includes a bare cell, a protection circuit module, and an upper case. The protection circuit module is attached to one surface of the bare cell, and the upper case is attached to cover the protection circuit module. An upper case of a conventional pack-type secondary battery is formed of a synthetic resin injection-molded material, so the secondary battery suffers from the following problems:
First, a conventional upper case is formed of an injection-molded material, and therefore cannot have a thickness thinner than that required for an injection molding process. For this reason, there is a limit to how much the secondary battery having the injection molded upper case can be downsized.
Second, there are problems in the outward appearance that are commonly observed in injection-molded materials. That is, drawbacks such as a weld line, s a thin line occurring at the junction of a resin upon injection molding, stress whitening of the product, and bubble marks occur in injection molded parts.